Gaines, James, McClellan, Jane and John Lawson were siblings, and were children of Piney Lawson. There is a lot of information at:http://jove.prohosting.com/~luvgwife/lawson.htm
The problem will be in figuring out the ancestry of the children of Piney--at least the three born before 1840--the children after 1840--James and Gaines--are often attributed to James Willis. Piney had two boys 10-15 and one girl 5-10 in 1840. This is likely to be John, McClellan and Jane in 1850. Some have speculated that Piney is the widow of an unknown son of Burrell Lawson.